13. A dishonest milkman professes to sell his milk at C.P. but he mixes it with water and thereby gains 25%. The percentage of water in the mixture is :

14. A merchant has 50 kg, of sugar, part of which he sells at 8% profit and the rest at 18% profit. He gains 14% on the whole. The quantity sold at 18% profit is :

15. Rs. 1000 is lent out in two parts, one at 6% simple interest and the other at 8% simple interest. The yearly income is Rs. 75. The sum lent at 8% is :